1- This current decays in time, so recency has a factor here. Any particular activation is biased according to recent inputs.
2- To my understanding it should not be about how many branches there are but how many frequent/significant ones there are. If there was few AC and lots of AB I do not see same columns representing both as a problem on the short term. On the opposite, maybe it should start like that.
What stops same columns representing A and B and C in the default Spatial Pooler? They get represented differently because there are mechanisms creating competitions among columns such as synapse adaptation, boosting, bumping synapse permanences based on activation frequency.
The most recent temporal pooling implementation that is published on Nupic is an extension of Spatial Pooling. So there is a competition among columns just as SP. If AB and AC appears distinctively enough some columns will specialize on the total overlap of A+B and some will specialize on A+C.
Pseudo-Pseudo Code
Published Implementation
Reservoir is just something I use not an official analogy but there were topics discussing temporal pooling implementations in the forums if you missed them. 1, 2
Maybe these would help clear things up a bit if I am not making sense.